1. Field of the Invention
The invention is related to communications, and in particular, to patch antennas for wireless communication devices.
2. Description of the Prior Art
Wireless communication devices are used by millions of people to communicate as they move around. These wireless communication devices provide many communication services, such as telephony and Internet access. To provide these communication services, wireless communication devices include antennas that exchange wireless communication signals with network systems. Some wireless communication devices have two antennas to provide wireless signal diversity. Wireless signal diversity is desirable, because if one wireless signal fades, the other wireless signal can still reach the receiving antenna.
In one antenna design, two antennas are arranged in parallel. For example, a “flip” type telephone may have two vertical antennas that are arranged in parallel in the upper portion of the telephone. Unfortunately, this antenna design has poor de-correlation. With poor de-correlation, the wireless communication signals from each antenna are too similar to provide adequate diversity. As a result, this type of antenna design does not effectively support advanced antenna techniques that require good de-correlation.
In another antenna design, two antennas are arranged perpendicular to one another. For example, a “flip” type telephone may have two perpendicular antennas, one in the upper portion of the telephone, and the other in the lower portion of the telephone. Unfortunately, this antenna design has poor equivalent gain. With poor equivalent gain, the signal strength in the channels of the wireless communication signal is different across the channels. As a result, this type of antenna design does not effectively support advanced antenna techniques that require good equivalent gain.
One example of an advanced antenna technique is referred to as Multiple Input Multiple Output (MIMO). MIMO antennas exchange multiple wireless communication signals for increased throughput as compared to a single channel. MIMO antennas provide excellent reliability and improved throughput by providing diverse signal paths. However, MIMO antennas require good equivalent gain and good de-correlation. Unfortunately, the antenna designs described above do not effectively support MIMO. Patch antennas with cross-polarized elements have good equivalent gain and good de-correlation. Thus, cross-polarized patch antennas could support advanced antenna techniques, such as MIMO. Unfortunately, current patch antennas are too large for use in relatively small wireless communication devices.